1. Field of the Invention
This invention relates to an auto focusing apparatus in a camera.
2. Related Background Art
There are known auto focusing apparatuses in cameras wherein the measurement of distances is effected in a plurality of areas in a photographing image field and a lens is driven to a distance selected from among them to thereby effect photographing.
In these auto focusing apparatuses, design is made such that one of a plurality of measured distance values obtained from said plurality of areas, which is on the nearest side, is selected. In the photographing of almost all persons, this makes it possible to take well-focused photographs.
However, where the object is a landscape or the like, it is not always desired to focus the camera on the closest object, and this has led to the disadvantage that the desired object is out of focus.
Further, in case of such photography as close-up photography in which the photographing magnification becomes great, the probability with which a main object is in the central portion of the photographing image field is high, but the main object is not always closest. When, the closest object is not a main object, there has been the disadvantage that if photographing is effected by ways of a conventional automatic distance measuring apparatus, the main object will be out of focus. In the case of close-up photography, the depth of field is very shallow.
There is also known an auto focusing apparatus in a camera wherein the distance to an object is measured from the phase difference between two object images formed on an image sensor, such as a CCD, through two optical systems.
In such a conventional auto focusing apparatus, the correlations between the two images on the image sensor are calculated while the two images are scanned in conformity with distance. A peak at which the correlations between the two images are most coincident with each other is found from the state of the variation in the correlation values, and this point is regarded as the distance to the object.
Also, whether this point should be adopted is determined on the basis of judgment values provided for the height of the peak of the correlations and the sharpness of the peak.
However, in a conventional auto focusing apparatus in a camera, if a periodic pattern, such as a plurality of objects similar in shape exist in the distance measuring field, there is a case where a different object is recognized as an identical object and an entirely wrong measured distance value is output (hereinafter referred to as false focusing). In such a case, there has been the problem that the focus deviates greatly.
This false focusing is liable to become particularly conspicuous when an originally far object is focused on the very near side by mistake.